Method of constructing a deformographic storage display tube

ABSTRACT

A method of manufacturing storage/display two chamber tubes by providing a molded soft glass envelope with a high outer shoulder at an open end and a low inner shoulder at the same end to form a trough in-between. The trough is filled with liquid metal, having a suitable melting point, such as indium, and the metal is allowed to solidify. A metal ring bearing a membrane for separating the two chambers one from another is placed on the solidified metal with air passages provided between the ring and the trough metal. A faceplate is sealed to the outer shoulder providing a closure of the second chamber and both chambers of the tube are then evacuated through a single tubulation. Finally, the tube is heated to bake out gasses trapped in the walls of the tube and to melt the trough metal. Upon melting, the metal ring settles into the trough metal forming a hermetic seal between the two chambers.

United States Patent Eldridge, Jr. et al.

METHOD OF CONSTRUCTING A DEFORMOGRAPHIC STORAGE DISPLAY TUBE Inventors: Arthur J. Eldridge, Jr., Stone Ridge; Arthur Sansom, West Hurley, both of NY.

International Business Machines Corporation, Armonk, NY.

Filed: May 31, 1973 Appl. No.: 365,665

Assignee:

References Cited UNITED STATES PATENTS 12/1971 Wohl et al 178/7.5 D Kozol et al l78/7.5 D

Primary ExaminerGranville Y. Custer, Jr. Assistant Examiner-James W; Davie Attorney, Agent, or FirmCharles E. Rohrer [5 7] ABSTRACT A method of manufacturing storage/ display two chamber tubes by providing a molded soft glass envelope with a high outer shoulder at an open end and a low inner shoulder at the same end to forr n a trough inbetween. The trough is filled with liquid metal, having a suitable melting point, such as indium, and the metal is allowed to solidify. A metal ring bearing a membrane for separating the two chambers one from another is placed on the solidified metal with air passages provided between the ring and the trough metal. A faceplate is sealed to the outer shoulder providing a closure of the second chamber and both chambers of the tube are then evacuated through a single tubulation. Finally, the tube is heated to bake out gasses trapped in the walls of the tube and to melt the trough metal. Upon melting, the metal ring settles into the trough metal forming a hermetic seal between the two chambers.

3 Claims, 4 Drawing Figures SOFT GLASS MOLDED ENVELOPE l0 PATENTEU 8 SHEET-10f 2 w: RES 5523 a time: we:

PAIENIEDHBT 3.840.283

SEE! EN 2 Fl G 2 FACEPLATE PR'ORART 54 WELD/ 'PUMP 14a TARGET 22 ja WELD 151 j HARD GLASS 52 ENVELOPE 10 FIG. 3 54 FACEPLATE E 12 7\ 7 TROUGH 52.

SOFT GLASS MOLDED ENVELOPE 10 1 METHOD OF CONSTRUCTING A DEFORMOGRAPHIC STORAGE'DISPLAY TUBE This invention relates to storage/display tubes used for the visible presentation of information transduced from electrical information bearing signals and more particularly to method for constructing a two chamber storage/display tube.

CROSS REFERENCE TO RELATED PATENTS U.S. Pat. No. 3,109,062 to Clauer and Kuehler issued Oct. 29, 1963.

U.S. Pat. No. 3,445,707 to Hershoff and Gilvey issued May 20, 1969.

U.S. Pat. No. 3,626,084 to Wohl, I-Iawn and Medley issued Dec. 7, 1971.

BACKGROUND OF THE INVENTION The conventional method of providing a static visual display of information transmitted in the form of electrical signals is by means of a cathode ray tube having a phosphor coated face on which an electron beam impinges to produce a visible display. The beam carries information by undergoing modulation of either the intensity or the deflection of the electron beam. However, the use of phosphors for displays of the type contemplated herein, that is, storage as well as projection of the display, is not completely satisfactory.

As a consequence, tubes have been developed and are described in the above referenced patents wherein electron beams generated by electron guns of the type used in cathode ray tubes are directed to a dielectric target rather than a phosphor target. Electron deposition on the dielectric target provides an electrostatic charge pattern corresponding to the information which modulates the electron beam. That electrostatic charge pattern is reproduced on the opposite side of the target in a special material which deforms according to the quantity of electrostatic charge deposited on the dielectric surface. The deformed material may then be viewed through reflective or transmissive optics and visual perception may be maintained satisfactorily for a period of hours after the electron beam generating gun is turned off.

Prior art methods of constructing these tubes have been limited to the production of tubes in small quantities for laboratory experimentation and are unsuitable for tube production in quantity. Consequently, it is the general object of the present invention to provide a method for constructing storage/display two chamber tubes for economical manufacture of quality devices. Other objects and advantages of the invention will become apparent through the following description.

SUMMARY OF THE INVENTION The method of this invention calls for a soft glass molded envelope open at one end. At the open end an outer high shoulder is provided to act as a flange for joining the faceplate of the device to the envelope in sealed juxtaposition. Also at the open end, an inner lower shoulder is provided to form a trough between the two shoulders, the trough provided to hold suitable metal such as indium. The dielectric target membrane which divides the device into two chambers is mounted on a metal ring and the edges of the ring are placed in the trough on the surface of the indium. At least one air passage is provided under the metal ring to join the two chambers together so that evacuation may take place from either chamber and evacuate both simultaneously. The tube is then baked at a temperature which melts the indium with the ring sinking into the trough providing a hermetic seal between the two chambers.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, partly broken away, i]- lustrating a general arrangement of a deformographic storage display tube manufactured in accordance with DETAILED DESCRIPTION OF AN EMBODIMENT FIG. 1 illustrates a general arrangement of a deformographic storage display tube. The tube includes an evacuated envelope 10 of any suitable shape such as that of a conventional cathode ray tube having an electron gun and focusing system at one end and an enlarged transparent faceplate 12 at the other end. Individual write and erase guns are shown in separate necks extending from the envelope 10 and it may be noted that one of these necks is normally used as tubulation for the evacuation of the electron beam chamber. The write gun 14 includes a cathode l6 and a control grid 18 to which signals are applied to modulate the electron beam intensity in conventional fashion. The modulating input signals may be derived from any suitable source such as from video information signal circuits 20. The modulated electron beam is scanned across the surface of dielectric target 22 by deflection means such as a deflection yoke 24 disposed around the neck of the envelope 10 and controlled by sweep voltage generator 26. Although a video-type scanning system is shown, selective scanning or other displays may alternatively be generated by digital-type circuits, by character beam-type tubes or by any other circuits appropriate for a particular application.

An erase gun 28 operated by erase control circuits 30 is utilized for erasure of the electrostatic charge distribution pattern on the writing side of the target 22. Erase gun 28 may be mounted in a separate neck of the envelope l0 and directs a dispersed high intensity beam onto the target surface. Details of the beam focusing and accelerating system are not shown since they may assume any of a number of conventional forms.

- The outer periphery of the target 22 is mounted to the inner wall of the envelope 10 in appropriate sealed fashion (not shown in detail in FIG. 1) to define two separate and independent chambers 32 and 34 within the envelope 10. The sealed chamber 32 on the one side of the dielectric target 22 is called the electron beam chamber because it contains the write gun 14 and the erase gun 28 and associated components. The sealed chamber 34 on the other side of the dielectric target 22 from the chamber 32 extends between the target and the tube faceplate l2 and may be termed a deformographic film chamber since it contains a deformographic film 36.

A conductive reference potential plane is disposed adjacent the tube faceplate 12 within the film chamber 34 to define appropriate means for establishing a reference potential within an extended surface area spaced apart from and substantially co-extensive with the target 22. The reference potential plane in FIG. 1 comprises a conductive ground plane 38, specifically a coating of transparent conductive material on the inner surface of the faceplate 12. Other arrangements for the conductive ground plane may be used such as that shown in U.S. Pat. No. 3,676,588 referenced above.

Other details of the tube shown in FIG. 1 are described in U.S. Pat. No. 3,626,084 incorporated herein by reference and will notbe repeated here. It should be noted, however, that normally the dielectric target 22 is preferably made of mica and the metal ring to which the mica is attached is normally made from iron and nickel as described in U.S. Pat. No. 3,445,707 also referenced above.

While reflective optics may be used, if desired, the system illustrated in FIG. 1 is a transmissive optical system of the schlieren type. Light from a source 60, which in this instance comprises a projection lamp, is focused along an optical axis 62 by a condenser comprising a pair of lenses 64. The focused light passes through a schlieren aperture 66 which is shown as comprising a perforated metal screen and through the tube faceplate l2 and conductive ground plane 38 to the deformographic film 36 where it is refracted and diffracted by the deformations therein. Light passing through the film 36, the target 22 and an optically clear window 68 in the envelope reaches a projection lens 70. It is obvious that the tube faceplate 12 must also be of optically clear material.

FIG. 2 shows the assembly of the target into the tube according to prior art methods primarily used for laboratory development of deformographic storage display tubes. The target 22 which carries the deformographic film 36 is attached to a metal ring 146 which may be of an iron and nickel composition as previously mentioned which is welded at 151 to a metal piece 147. The shape of the ring 146 and the metal piece 147 together comprise a spring action around the weld 151 which provides for different coefficients of expansion between the metal ring 146 and the other metal elements in the tube construction. Metal piece 147 is joined through welding to flanges 148 and 149 at weld 150. These pieces must be suited to the coefficient of expansion of the glass members, faceplate 12 and hard glass envelope 10.

This prior art method of constructing the tube in the laboratory involves hand fabricating the envelope from hard glass and sealing it to the metal flanges 148 and 149. The tube is assembled by placing the target assembly between the flanges of the faceplate and the main envelope and welding the three pieces together with a heliarc welder. The tube is then pumped down through the pumping tubulation 152 evacuating one chamber and through a second tubulation which may be through the write or erase gun necks as previously mentioned. Thus, the two chambers are evacuated independently and must be processed on a special two-port pumping system. This is an expensive method of building the tube and is less practical for production items. Also, because the mica target disk is under tension, any nonuniform strain which may be imposed on the target support ring tends to cause the target to wrinkle. Such strains may be introduced during welding or'during evacuation of the tube.

FIG. 3 shows the assembly of the target into the tube manufactured through the method of this invention.

Target 22 with deformographic film 36 is once again mounted on a metal ring 146. The end of ring 146 is placed in the trough 154 where a hermetic seal is formed around the end of ring 146 by a metal filling the trough, such metal may be indium. Chamber 34 is formed by the faceplate 12 joined to shoulder 155 through seal 153. Seal 153 may be formed through an epoxy compound such as AMCON 420 manufactured by the American Cyanimid Corporation, Number WE4527D3. Considerations for the selection of an appropriate epoxy would be the length of time needed to cure the compound at a temperature below that which would damage the target in air. For those deformographic materials in present use, curing should take place below 180 C and where indium is the metal selected for the seal at the trough 154, the cure must be below the melting point of indium which is approximately l56 C. Obviously, an epoxy which cures at room temperature could be used, however, the time to cure such an epoxy normally is lengthy. The particular epoxy compound mentioned above cures at C in approximately 2 hours.

Trough 154 is located in the open end of the soft glass molded envelope 10 formed between an outer high shoulder 155 and an inner lower shoulder 156. The metal to be used for the seal may be indium which has a melting point of 156 C or an alloy of indium which might carry a melting point of between C and 300 C. Normally these indium alloys are various percentage mixtures of indium and tin, indium and bismuth, indium and lead, and indium and various combinations of those three other elements.

The method by which the tube is put together will now be described. The assembly starts with a molded soft glass envelope similar to that used for an ordinary cathode ray or television tube. The envelope is made with the shoulders 156 and forming the trough 154. After wetting the surfaces of the trough by wiping melted indium on the surfaces, the trough is partially filled with indium metal or an indium alloy or any other suitable metal. The indium is arranged in such a way as to support the target ring and provide a path for free air flow around the target assembly during pump-down. This is done by partially filling the trough 154 with melted indium, allowing the indium to solidify, then placing the target ring 146 carrying membrane 22 on the surface of the solidified indium. As noted for the surfaces of the trough, the lower portion of the ring ina simple mechanism such as placing pieces of indium wire on the surface of the solidified indium and then placing the target ring on the indium wire. Should the notches 160 shown in FIG. 4 be the construction utilized to provide the free air flow, care must be taken that these notches will sink into the trough when the indium melts and be completely covered by the surface level of the melted indium in trough 154. lt should be noted that'the prewetting operation mentioned above is performed because of peculiarities of indium in that binding to the trough and ring to form a hermetic seal requires prewetting.

After the metal ring 146 is placed on the solidified indium, the next step in the method is to evacuate the two chambers of the tube through a tubulation which may normally be in the write gun stem. Evacuation may be carried out through commercially available diffusion pumps normally .used in cathode ray tube manufacture. When the vacuum in the tube has reached an appropriate level which may be, for example, Torr, the tube may be heated in a baking operation to accelerate the outgassing of any gases trapped in the walls of the tube. Temperature for the baking operation may be slightly above the melting point of the metal placed in the trough but must not be so high as to damage the target. Typical bake-out temperatures may be from 140 to 200 C. During this bake-out, the indium or other metal melts and the target ring 146 settles into the trough 154 forming a hermetic seal between the two chambers. When the outgassing is complete, the tubulation is closed and the tube is allowed to cool. During cooling, the indium solidifies forming the mechanical connection which separates the two chambers. Because the mechanical connection is made after the envelope has been evacuated, any deformations which occur in the envelope during pumping will not be transmitted to the target assembly. This eliminates the wrinkling of the target membrane which has occurred during pump-down in prior art methods.

Thus, a method of construction has been provided which reduces the cost of tube parts, notably the use of soft glass rather than hard glass, reduces the amount of hand work, reduces the number of metal rings, eliminates two known causes of tube loss (welding and target distortion during pump-down) and allows the tube to be evacuated on conventional type CRT processing equipment instead of special two-port pumping stations.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

l. A method of constructing a two chamber storage/- display tube wherein said two chambers are sealed one from another by a membrane mounted on a metal ring, said method comprising the steps of a. supplying a molded soft glass envelope with an open end, said envelope including at said open end an outer high shoulder and an inner low shoulder with a trough formed in-between said two shoulders,

b. partially filling said trough with liquid metal and allowing said metal to solidify,

0. providing means for an air path between said ring and said solidified trough metal when said ring is placed in said trough,

d. placing said ring in said trough, thus forming a first chamber,

e. attaching a faceplate in sealed juxtaposition to said outer shoulder, thus forming a second chamber,

f. evacuating both chambers of said tube from a single tubulation, then g. heating said tube at a temperature sufficient to melt said trough metal but not so high as to damage said membrane, allowing said ring to settle into said melted metal to form a hermetic seal between said two chambers.

2. The method of claim 1 wherein said trough metal is indium or an indium alloy.

3. The method of claim 1 wherein said air path is provided by notches in said metal ring, said notches being completely covered when said ring settles into said trough during step g. 

1. A method of constructing a two chamber storage/display tube wherein said two chambers are sealed one from another by a membrane mounted on a metal ring, said method comprising the steps of a. supplying a molded soft glass envelope with an open end, said envelope including at said open end an outer high shoulder and an inner low shoulder with a trough formed in-between said two shoulders, b. partially filling said trough with liquid metal and allowing said metal to solidify, c. providing means for an air path between said ring and said solidified trough metal when said ring is placed in said trough, d. placing said ring in said trough, thus forming a first chamber, e. attaching a faceplate in sealed juxtaposition to said outer shoulder, thus forming a second chamber, f. evacuating both chambers of said tube from a single tubulation, then g. heating said tube at a temperature sufficient to melt said trough metal but not so high as to damage said membrane, allowing said ring to settle into said melted metal to form a hermetic seal between said two chambers.
 2. The method of claim 1 wherein said trough metal is indium or an indium alloy.
 3. The method of claim 1 wherein said air path is provided by notches in said metal ring, said notches being completely covered when said ring settles into said trough during step g. 